Optically transparent ceramic materials have numerous applications such as in infrared sensors, transparent armor, and high power ceramic lasers. Mechanical and thermal shock resistant capabilities of ceramic materials are generally limited by their mechanical strength. It is generally accepted that the strength of a ceramic material is correlated to its grain size, with the strength of a ceramic inversely proportional to the final grain size. Thus, the strength of transparent ceramics can be largely improved simply by reducing their grain size. For example, the ballistic performance of oxide ceramics is known to be improved by the achievement of finer grain sizes in sintered products. Moreover, large grained materials tend to exhibit a lower mechanical strength than smaller grain-sized materials. Also, larger grained materials are less desirable in applications demanding high thermal shock resistance, such as high-energy laser systems that can generate significant heat loads. One way to improve the strength of ceramics is to develop ultrafine, preferably nanoscale, grain sizes. Nanosized starting powder thus offers the possibility of producing very fine grain sizes in transparent ceramic materials, thus providing higher mechanical strength and thermal shock resistance.
Various methods, including combustion synthesis, laser ablation, microwave plasma synthesis, precipitation from a solution, spray pyrolysis, and plasma arc synthesis have been reported to produce ceramic nano-powders. Although these methods are generally purported to provide high quality nano-powders, they have proved unsuccessful in producing un-agglomerated/un-aggregated nano-powders with mono-disperse and narrow sized distribution. For example, the flame spray pyrolysis is a well-known nano-powder production technique in which has been regarded as potentially producing non-agglomerated or weakly agglomerated nano-powder. However, in practice it tends to produce powders composed of mixture of broad size distribution in which the size of powders ranging from 10's of nanometers to few hundred microns. This results in larger grain sizes upon densification, e.g. when making ceramics. Another example of making nano-powder is by combustion synthesis method. It is known that nanosized powders are produced through the combustion of metal precursors and organic fuels such as citric acid and urea. This synthesis route is relatively cost effective and convenient. However, this method also suffers from drawback that the powders are composed of various sizes of particles of 100's of nanometer to a few hundreds of micron.
A need exists nano-scale metal oxide powders having a narrow size distribution.